1. Field of the Invention
The present invention relates to the field of infusion monitoring and alarm devices, and more specifically, a portable, yet accurate alarm monitor.
2. Prior Art
One important and frequently utilized medical procedure is the intravenous infusion of a variety of fluids, such as whole blood, plasma, dextrose, physiologic saline, and other medication. However, several problems are associated with this procedure. One difficulty is that of accurately administering some portion of a standard unit of such fluids; that is, with the typical intravenous injection system it is difficult to terminate the infusion, after some predetermined quantity of fluid has been administered, without frequent, time consuming, observations of the quantity of remaining solution. This requires frequent checking of the fluid level by trained personnel, such as a nurse. Another problem associated with intravenous infusion is that the complete injection of one unit of fluid may be accomplished without notification of the attending personnel. Thus, when continuous administration is required, completion of one stage of such administration may go unnoticed, resulting in some period of time before it becomes known that all the fluid has been infused into the patient. Beyond this undesirable lapse in time, the termination of the injection may result in clotting and occlusion of the needle, which has been supplying the intravenous solution, due to backflow of the patient's blood into the needle; this would necessitate removal, location of another vein, and another insertion. Accordingly, is has been necessary that constant attention be given to the patient when receiving an infusion.
What is required to solve the problems noted above is an infusion monitoring device which will provide a warning signal when the infusion has progressed to some predetermined extent such that when it is desired to administer only a portion of a standard unit of solution, the monitoring device may be adjusted such that an alarm will be given prior to or at the exact completion of the desired infusion. When it is desirous to administer a complete unit of liquid, the device should be adjustable such that an alarm will be given prior to the complete infusion of one standard unit of such liquid or solution; a new supply of fluid may then be provided without breaking the continuity.
However, beyond this signaling capability, a monitoring device should also have an initial and a long-term accuracy so that over its useful life it may be used with confidence. If initially or after a long period of use, this sensing is not performed accurately, when it is being used to signal that the desired amount of solution has been infused, inaccurate administration will result--either too little or too much intravenous solution will have been infused. If too little fluid has been infused, only inconvenience to attending personnel will result, but if too much fluid has been administered, the patient may suffer adverse consequences. And, when the device is being used to signal that the infusion of one unit of solution is near completion, the alarm will be given either prematurely, again resulting in wasted effort by those notified by the alarm, or after the complete infusion of one unit, resulting in possible clotting and occlusion of the needle. Manifestly, if such initial and long-term accuracy is not maintained, the problems of infusion noted above will be aggravated and ultimately the use of the device will be severely diminished. Finally, to provide maximum useful life, and consequently minimum expense, the monitoring device should be simply constructed, utilizing direct and effective design principles, and should be easily portable.
Devices which monitor the infusion of intravenous solutions and provide a warning when such infusion has reached a predetermined extent are well known in the art. These devices usually utilize some form of spring extension which provides, in effect, a weighing of the slowly decreasing supply of fluid. In these devices a switch means is provided which acutates a warning signal when the weight of the fluid being administered has reached the desired level. While these devices may have initially provided accurate signaling capability, their inherent design principle of weight sensing by spring extension has failed to provide the requisite long-term accuracy. This failure is due to the ever-increasing fatigue of the spring caused by its repeated extension. Over a period of time this fatigue results in a change in the spring constant; that is, the reaction of the spring to a given force varies as the degree of fatigue increases. Thus, as these devices are used, the setting which initially provided a signal at the desired fluid level no longer provides a signal at that level. Moreover, many of these devices are relatively complex and are therefore expensive.
One prior art attempt to provide the capabilities noted above is described by O'Neill, U.S. Pat. No. 3,390,238. O'Neill utilizes an extension spring-biased member having a hook portion for supporting an intravenous container. Associated with the spring-biased member is an arm which, upon the contents of the container reaching a predetermined level, is adapted to make an electrical contact so as to actuate an alarm system. Another prior art monitoring device is disclosed by Hulse et al, U.S. Pat. No., 3,389,387. Hulse also utilizes an extension spring-biased member which supports an intravenous container by a hook portion. Associated with the spring-biased member is an actuator, adapted to actuate a conventional microswitch when the intravenous container weight, and thus the fluid level, has reached a predetermined level. In both the O'Neill and Hulse devices, the problem of long-term accuracy was not effectively solved as their device's level adjustment repeatability will shift with usage due to spring fatigue. Further, these prior art devices fail to meet the previously discussed requirements of simplicity and inexpensiveness.
In the present invention the problem of long-term accuracy is solved by utilizing a simple but effective weighing system whose principle design feature is that of spring compression, not spring extension. This feature greatly minimizes spring fatigue, thus minimizing spring constant shift and consequently providing long-term accuracy of level threshold. Moreover, the present invention provides a device which is both inexpensive and uncomplicated to produce, and utilizes an electrical plug system which permits various quantities of fluid to be administered without complex adjustment of the device.